Plied cord rope construction



Feb. 14, 1961 D. HIMMELFARB ETAL PLIED CORD ROPE CONSTRUCTION Filed Oct.16, 1956 x E. l

T m1 T .6 MMJ ZM f1 5. fii

2,971,321 PLIED CORD ROPE CONSTRUCTION David Himmelfarb, 117 BeaumontAve., Newton, Mass, and William J. Kaes, 192 Union St., Randolph, Mass.

Filed on. 16, 19 56, Ser. No. 616,356 12 Claims. (Cl. 57-139) (Grantedunder Title 35, US. Code (1952), sec. 266) The invention describedherein may be manufactured and used by or for the. Government of theUnited States of America for governmental purposes without the paymentof any royalties thereon or therefor.

This invention relates to ropes and methods of making ropes. Inparticular the invention relates to stranded ropes of man-made ornatural fibers and to methods of making such ropes. For example, itrelates to the structure and fabrication of ropes made from man-madefibers of which nylon, Dacron, Orlon, polyethylene, etc. are examples,and natural fibers, of which manila, sisal, etc. are examples, bytwisting the fibers into yarns, sometimes called threads; twisting twoor three of the yarns together into a cord; twisting a number ofcordstogether into strands, and the strands into rope.

An object of the inventionis to provide a rope and method of makingsame.

Another object is to provide a stranded rope of manmade or naturalfibersin which thestrands are made from a balanced cord structure and furtherto provide a method of making same.

Another object is .to provide a stranded rope of manrnade or naturalfibers in which there is imparted to the strands a twist reservoir forthe acquisition of additional twist associated with the stresses andstrains of service whereby the effects of such stresses and strains canbe absorbed without deformation of the strands and development of kinks,bulges and cockles.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood .byreference to the following detailed description when considered inconnection with the accompanying drawing wherein;

Fig. 1 is a diagrammatic .view showing a plurality of filaments ofman-made or natural fiber.

Fig. 2 is a diagrammatic view showing the filaments twisted into aplurality of yarns.

Fig. 3 is a diagrammatic view showing. the yarns twisted into a cord.

Fig. 4 is a perspective view of the yarn in Fig. 3 that is partlyuntwisted at the left end for clarity of illustration.

Fig. 5 is a diagrammatic view showing a plurality of cords.

Fig. 6 is a diagrammatic view showing the cords twisted into a strand.

Fig. 7 is a diagrammatic view showing the strands twisted into a rope,and.

Fig. 8 is a perspective view of the rope in Fig. 7 that is partlyuntwisted at the left and for clarity of illustration.

Conventional rope structures are formed by a successive reversal ofdirection of twist of components related to the twisted structure. Whenthe filaments or fibers are twisted into yarns in manner such that thespiral of the twist is upward to the right (also termed right twist or Ztwist), the strands are formed bytwisting a number of such yarnstogether in the reverse direction nited States Patent so that the spiralof the twist is upward to the left (also termed left twist or S twist).The rope is completed by twisting three or more strands in reversedirection so the spiral of the twist is upward to the right. By thisprocess of reversal of twist, the filaments or fibers become compactedinto a structurally balanced form, designated the rope, required for theservice intended.

When such conventional rope is placed in service, the structural balanceis upset by conditions of service. Tension tends to untwist the rope bytending to untwist the group of strands. But because of the reversal oftwist between rope and strands, each individual strand becomes twistedmore tightly and thereby harder. With increase in tension this effectcontinues until there results an internal rearrangement in the structureof the strand, with the resulting deformation manifesting itself by theappearance of kinks and bulges, also termed cockes. These deformationsresult in a loss of strength and reduce the serviceability of the rope.Wetting will swell the rope to increase the girth and this will have theeffect of hardening and tightening the rope to thereby increase thedegree of twist and make the strand even more liable to kinks and bulgeswhen tension is applied in service or when rope is handled duringservice operations.

Conventional ropes of man-made fiber such as nylon, Dacron and Orion,when exposed to the weather and sunlight, will shrink and tighten therope structure to further reduce serviceability. Attempts at overcomingthese adverse efiects by reducing the relative amount of twist in thestrands and ropes has developed other defects it has been establishedthat where degrees of twist employed are comparable, such ropes ofman-made fiber are not sutficiently compact in structure for properserviceability. The additional twist to provide the additionalcompacting and hardness is necessarily of such magnitude as to affordlittle opportunity to absorb the shifting stresses in service so thatdeformation of strands is accelerated. In the process known as heatsetting, the strands or yarns of the man-made fibers are stabilized byexposure to hot water, steam, or dry heat, so that the resultingshrinkage serves to provide additional compacting and hardness. However,the shrinkage in this case is of magnitude such as to result indeformation of the strands with consequent kinks and bulges.

The present invention overcomes these defects to produce a rope whichwill, in general, possess the attributes of a rope properly compactedand hardened by twist for greater serviceability, but which will remainserviceable and resist the strand deformation and its associated kinksand bulges when subject to service stresses and strains. Our inventionmarks a sharp departure from conventional ropes by providing a balancedcord structure for twisting into strands in place of the unbalancedtwisted yarn structure conventionally em ployed for twisting intostrands. The term cord we define as a flexible, continuous braided ortwisted structure formed from yarn and adapted to be twisted intostrand, generally less than inch diameter and having the yarn twiststructurally balanced against the cord twist to maintain compactness.The balance is evidenced by the restraint of freely twisting back onitself when the two parallel sides of an extended loop of the cord arein proximity to one another. By this balanced cord construction, adesired compacting can be attained with considerably less twist in thestrand, so that there is imparted to the strand a twist reservoir forthe acquisition of additional twist associated with the stresses andstrains of service, whereby the effects of such can be absorbed withoutdeformation of the strands and development of kinks, bulges and cockles.The compacting effect may be regulated by the extent of twist in thecord in relation to the strand.

In practicing the invention to make a rope of nylon, for example, thenylon filaments 11 shown in Fig. 1 are bunched into ribbons 12 which aretwisted into yarns 13. For convenience of illustration yarns 13 areshown as having 8 twist. The amount of twist will be determined by thediameter of the yarn and may be varied to increase or lessen thecompacting effect of the twist. We have found the following relationshipto exist:

Tan 6=turns per inch diameter of yarnXvr where is the helical angle oftwist. The value of 0 will ordinarily be in the range of 15 to 25.

Two or more yarns 13 are next twisted into cord 14 by a laying operationin 2 direction reverse to the direction of S twist of the yarns 13. Bythis process, the yarn S twist is maintained relative to the cord 2twist, so that the cord 14 is structurally balanced as previouslydescribed. The state of balance we have found to exist when the Z twistin the cord 14 is within the range of 70 to 85 percent of the S twist inthe yarn 13. While nylon has been indicated in the foregoingillustration, the structure of the cord 14 and the twist relationship isequally applicable to man-made fibers such as Orlon, Dacron,polyethylene, and natural fibers such as manila and sisal.

The formation of the strands 15 from the cords 14 is illustrated inFigs. and 6. In forming the strands 15,

a number of cords 14 are twisted together in the usual S twist reverseto the Z twist of the cord 14. A forming tube (not shown) usual to theart is employed. It has been our experience that the relationshipbetween the number of cords 14 and the dimension of the bore of the tubeis critical to appearance and performance of the rope. Such relationshipwill vary according to the degree of compactness of the cord 14, itssize, the smoothness of its surface, and the nature of the fiber. Forone type of nylon cord 14 laid with an angle of twist of 20 andconsisting of three yarns 13, each 15,120 denier in size, therelationship has been established according to the following:

where D is the bore dimension in inches (range 0.60 to 1.2 inches) and Nthe number of such cords 14. Similar relationships have been determinedfor other cords of natural and man-made fibers in other sizes to reflectthe variable factors cited. The distribution of the cords 14 withrespect to arrangement within a strand 15 We have found also to becritical to appearance and performance of the rope. The layer of cords14 comprising the surface of the strands 15 we have found also dependentupon the degree of compactness of the cord 14, its size, the smoothnessof its surface, and the nature of the fiber. The average relationshipfor most cords 14, with adjustment to reflect the variable factorscited, we have found to be:

Number of surface yarns=% where D is the tube bore dimension in inches,and d is the diameter in inches of the cord 14. The turns imparted tothe strand 15 will be determined by the ultimate compactness andhardness of the rope 16, which is to 'be attained by twisting three ormore strands 15 together, and cannot be defined by specific formulation,but rather must be incorporated according to the judgment and art of theropemaker. It has been our experience that for a given compactness andhardness of rope structure, the strand man-made fibers such as nylon,Dacron and Orlon will require a greater degree of twist than the naturalfibers such as manila and sisal. One type of nylon, for example, willrequire a strand turn or length of spiral pitch -85 percent of twistrequired for manila of comparable size. The term filament is intended toinclude not only continuous filaments but also filaments made of staplefibers.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

We claim:

1. The method of forming a stranded rope structure which comprisessuccessively twisting in one direction a plurality of fibers orfilaments into yarn, twisting in the opposite direction a plurality ofyarns, preferably three, into a cord which is in balance in relation tothe torsional forces manifest between the yarns and the cord, twistingin said one direction a plurality of cords into a strand, and twistingin said opposite direction a plurality of strands into a rope.

2. The method of forming a stranded rope structure which comprisessuccessively twisting in one direction a plurality of thermoplasticfilaments into yarn, twisting in the opposite direction a plurality ofyarns into a cord which is in balance in relation to the torsionalfore-es manifest between the yarns and the cord, twisting in said onedirection a plurality of cords into a strand, and twisting in saidopposite direction a plurality of strands into a rope.

3. The method of forming a stranded rope structure, which comprisessuccessively twisting in one direction a plurality of fibers orfilaments into yarn with a helical angle of twist of about 15 to 25,twisting a plurality of such yarns in a reverse direction into a cord indegree to balance the opposing torsional forces manifest between theyarns and the cord, twisting a plurality of such cords into a strand indirection reverse to the twist of each cord, and twisting a plurality ofsuch strands in direction reverse to that in each strand into a rope butwith a moderate amount of twist to attain flexibility.

4. The method of forming a stranded rope which comprises successivelytwisting a plurality of fibers or filaments into yarns with a helicalangle of twist of about 15 to 25 twisting a plurality of such yarns,preferably three, together in reverse direction into a cord, the degreeof twist measuredby the turns per foot amounting to 70 to percent of theturns per foot of the component yarns, thereby effecting balance betweenthe opposing torsional forces manifest between the cord and thecomponentyarns, twisting a plurality of such cords into a strand in directionreverse to the twist of each cord, and twisting a plurality of suchstrands in reverse direction to each strand, into a rope with moderatetwist to attain flexibility.

5. A rope comprising a plurality of strands twisted together, eachstrand being formed of a plurality of cords twisted together, each cordbeing formed of a plurality of yarns twisted together, and each yarnbeing formed of a plurality of filaments twisted together, the directionof twist varying alternately from filaments to yarn, yarn to cord, cordto strand, and strand to rope, and the twist in the yarns and cordsbeing balanced with respect to the torsional forces manifest between theyarns and the cords.

6. The rope as set forth in claim 5, wherein the helical angle of twistof the filaments into yarn is about 15 to 25 7. The method of making astranded rope which comprises twisting a plurality of filaments intoyarns, twisting a plurality of such yarns into cords, and twisting aplurality of such cords into strands, twisting at least three of suchstrands into a rope, varying the direction of twist alternately fromfilament to yarn, yarn to cord, cord to strand, and strand to rope, andbalancing the twist in the yarns and cords to provide a balanced cord.

8. A rope comprising a plurality of strands twisted together, eachstrand being formed of a plurality of cords twisted together, each cordbeing formed of a plurality of yarns twisted together, and each yarnbeing formed of a plurality of filaments twisted together, the directionof twist varying alternately from filaments to yarn, yarn to cord, cordto strand, and strand to rope, and the twist in the cord being withinabout 70 to 85 percent of the twist in the yarns.

9. The rope as set forth in claim 8 wherein the helical angle of twistof the filaments into yarn is about 15 to 25.

10. A rope comprising a plurality of strands twisted together, each suchstrand being formed of a plurality of cords twisted together, each suchcord being formed of a plurality of yarns twisted together, each suchyarn being formed of a plurality of filaments twisted together, thedirection of twist varying alternately in opposite directions fromfilament to yarn, yarn to cord, cord to strand and strand to rope, thetwist of the filaments into yarn making a helical angle of twist ofabout 15 to 25, the degree of twist of the yarns in each cord, measuredby turns per foot, amounting to about 70 to 85 percent of the turns perfoot of the component yarns to efiect a balance between the opposingtorsional forces manifest between the cord and the component yarns.

11. A rope comprising a plurality of strands twisted together, each suchstrand being formed of a plurality of cords twisted together, each suchcord being formed of a plurality of yarns twisted together, each :suchyarn being formed of a plurality of filaments twisted together, thedirection of twist varying alternately in opposite directions fromfilament to yarn, yarn to cord, cord to strand and strand to rope, thetwist of the filaments into yarn making a helical angle of twist ofabout 15 to 25, each yarn twist being structurally balanced against thecord twist, and the amount of twist per unit length in the strands andrope being less than in said cords to provide a twist reservoir in thestrands for the acquisition of additional twist from the stresses andstrains of service.

12. The rope as set forth in claim 11, wherein said rope is formed of atleast three yarns.

References Cited in the file of this patent UNITED STATES PATENTS2,343,892 Dodge et al Mar. 14, 1944 2,346,759 Jackson et al Apr. 18,1944 FOREIGN PATENTS 543,974 Great Britain Mar. 23, 1942 OTHERREFERENCES Book entitled The Practical Rope Maker, George Lawrie, firstedition, 1948; pages 42 and G 105. (Copy available in Division 21.)

